Genetic and environmental mechanisms underlying stability and change in problem behaviors at ages 3, 7, 10, and 12

Childhood trajectories of emotional and behavioral difficulties are related to polygenic liability for mood and anxiety disorders

BACKGROUND

Symptoms related to mood and anxiety disorders (emotional disorders) often present in childhood and adolescence. Some of the genetic liability for mental disorders, and emotional and behavioral difficulties seems to be shared. Yet, it is unclear how genetic liability for emotional disorders and related traits influence trajectories of childhood behavioral and emotional difficulties, and if specific developmental patterns are associated with higher genetic liability for these disorders.

METHODS

This study uses data from a genotyped sample of children (n = 54,839) from the Norwegian Mother, Father, and Child Cohort Study (MoBa). We use latent growth models (1.5-5 years) and latent profile analyses (1.5-8 years) to quantify childhood trajectories and profiles of emotional and behavioral difficulties and diagnoses. We examine associations between these trajectories and profiles with polygenic scores for bipolar disorder (PGSBD), anxiety (PGSANX), depression (PGSDEP), and neuroticism (PGSNEUR).

RESULTS

Associations between PGSDEP, PGSANX, and PGSNEUR, and emotional and behavioral difficulties in childhood were more persistent than age-specific across early childhood (1.5-5 years). Higher PGSANX and PGSDEP were associated with steeper increases in behavioral difficulties across early childhood. Latent profile analyses identified five profiles with different associations with emotional disorder diagnosis. All PGS were associated with the probability of classification into profiles characterized by some form of difficulties (vs. a normative reference profile), but only PGSBD was uniquely associated with a single developmental profile.

CONCLUSIONS

Genetic risk for mood disorders and related traits contribute to both a higher baseline level of, and a more rapid increase in, emotional and behavioral difficulties across early and middle childhood, with some indications for disorder-specific profiles. Our findings may inform research on developmental pathways to emotional disorders and the improvement of initiatives for early identification and targeted intervention.

The stability and change of wellbeing across the lifespan: a longitudinal twin-sibling study

BACKGROUND

Wellbeing is relatively stable over the life span. However, individuals differ in this stability and change. One explanation for these differences could be the influence of different genetic or environmental factors on wellbeing over time.

METHODS

To investigate causes of stability and change of wellbeing across the lifespan, we used cohort-sequential data on wellbeing from twins and their siblings of the Netherlands Twin Register (NTR) (total N = 46.885, 56% females). We organized wellbeing data in multiple age groups, from childhood (age 5), to adolescence, up to old age (age 61+). Applying a longitudinal genetic simplex model, we investigated the phenotypic stability of wellbeing and continuity and change in genetic and environmental influences.

RESULTS

Wellbeing peaked in childhood, decreased during adolescence, and stabilized during adulthood. In childhood and adolescence, around 40% of the individual differences was explained by genetic effects. The heritability decreased toward old adulthood (35-24%) and the contribution of unique environmental effects increased to 76%. Environmental innovation was found at every age, whereas genetic innovation was only observed during adolescence (10-18 years). In childhood and adulthood, the absence of genetic innovation indicates a stable underlying set of genes influencing wellbeing during these life phases.

CONCLUSION

These findings provide insights into the stability and change of wellbeing and the genetic and environmental influences across the lifespan. Genetic effects were mostly stable, except in adolescence, whereas the environmental innovation at every age suggests that changing environmental factors are a source of changes in individual differences in wellbeing over time.

Associations of Perinatal Metal and Metalloid Exposures with Early Child Behavioral Development Over Time in the New Hampshire Birth Cohort Study

Research on the neurodevelopmental effects of metal(loid)s has focused mainly on outcomes assessed at one time point, even though brain development progresses over time. We investigated biomarkers of perinatal exposure to metals and changes in child behavior over time. We followed 268 participants from the prospective New Hampshire Birth Cohort Study between birth and age 5 years. We measured arsenic (As), copper (Cu), manganese (Mn), lead (Pb), selenium (Se), and zinc (Zn) in toenails from 6-week-old infants. The Behavioral Symptoms Index (BSI), externalizing, and internalizing symptoms were assessed using the Behavior Assessment System for Children, 2nd edition (BASC-2) at ages 3 and 5 years. Multivariable linear regression was used to estimate associations of metals with behavior change, calculated as the difference in symptom raw scores between 3 and 5 years, in addition to the associations for symptom scores at 3 and 5 years separately. Sex-specific associations were also explored using stratified models and a sex-metal interaction term. Adjusted associations of metals and change in behavior varied by exposure and outcome. Each 1 μg/g increase in ln toenail Cu was associated with improved behavior between 3 and 5 years [BSI: β = - 3.88 (95%CI: - 7.12, - 0.64); Externalizing problems: β = - 2.20 (95%CI: - 4.07, - 0.33)]. Increasing Zn was associated with increased externalizing behavior over time (β = 3.42 (95%CI: 0.60, 6.25). Sex-stratified analyses suggested more pronounced associations among boys compared to girls. Perinatal exposure to metals may alter behavioral development between ages 3 and 5 years. Findings support the need for more research on associations between metals and neurodevelopment over longer time periods.

Developmental profiles of child behavior problems from 18 months to 8 years: The protective effects of structured parenting vary by genetic risk

Some children are more affected by specific family environments than others, as a function of differences in their genetic make-up. However, longitudinal studies of genetic moderation of parenting effects during early childhood have not been conducted. We examined developmental profiles of child behavior problems between 18 months and age 8 in a longitudinal parent-offspring sample of 361 adopted children. In toddlerhood (18 months), observed structured parenting indexed parental guidance in service of task goals. Biological parent psychopathology served as an index of genetic influences on children's behavior problems. Four profiles of child behavior problems were identified: low stable (11%), average stable (50%), higher stable (29%), and high increasing (11%). A multinominal logistic regression analysis indicated a genetically moderated effect of structured parenting, such that for children whose biological mother had higher psychopathology, the odds of the child being in the low stable group increased as structured parenting increased. Conversely, for children whose biological mother had lower psychopathology, the odds of being in the low stable group was reduced when structured parenting increased. Results suggest that increasing structured parenting is an effective strategy for children at higher genetic risk for psychopathology, but may be detrimental for those at lower genetic risk.

Exposure to family stressful life events in autistic children: Longitudinal associations with mental health and the moderating role of cognitive flexibility

Mental health problems are prevalent in autistic youth, but the underpinning mechanisms are not well explored. In neurotypical youth, stressful life events are an established risk factor for mental health problems. This study tested longitudinal bidirectional associations between family-level stressful life events and mental health problems and whether these were moderated by cognitive flexibility, in a cohort of autistic children (N = 247). Family-stressful life events, assessed using the parent-reported Family Inventory of Life Events and Changes, and mental health problems, assessed using the teacher-reported Child Behavior Checklist Internalizing and Externalizing Symptoms subscales, were measured at multiple points between 7 and 11 years. Analyses showed no significant pathways from internalizing or externalizing symptoms to family-stressful life events or from family-stressful life events to internalizing or externalizing symptoms. There was some evidence of moderation by cognitive flexibility; the family-stressful life events to internalizing symptoms pathway was non-significant in the group with typical shifting ability but significant in the group with clinically significant shifting problems. Information about family-level stressful life event exposure and cognitive flexibility may be helpful in identifying autistic youth who may be at higher risk of developing mental health problems. Established risk factors for mental health problems in neurotypical populations are relevant for understanding mental health in autistic youth.

Continuity and Change in the Genetic and Environmental Etiology of Youth Antisocial Behavior

Trajectories of youth antisocial behavior (ASB) are characterized by both continuity and change. Twin studies have further indicated that genetic factors underlie continuity, while environmental exposures unique to each child in a given family underlie change. However, most behavioral genetic studies have examined continuity and change during relatively brief windows of development (e.g., during childhood but not into adolescence). It is unclear whether these findings would persist when ASB trajectories are examined across multiple stages of early development (i.e., from early childhood into emerging adulthood). Our study sought to fill this gap by examining participants assessed up to five times between the ages of 3 and 22 years using an accelerated longitudinal design in the Michigan State University Twin Registry (MSUTR). We specifically examined the etiologies of stability and change via growth curve modeling and a series of univariate and bivariate twin analyses. While participants exhibited moderate-to-high rank-order stability, mean levels of ASB decreased linearly with age. Genetic and nonshared environmental influences that were present in early childhood also contributed to both stability and change across development, while shared environmental contributions were negligible. In addition, genetic and nonshared environmental influences that were not yet present at the initial assessment contributed to change over time. Although ASB tended to decrease in frequency with age, participants who engaged in high levels of ASB during childhood generally continued to do so throughout development. Moreover, the genetic and nonshared environmental contributions to ASB early in development also shaped the magnitude of the decrease with age.

How nonshared environmental factors come to correlate with heredity

Conventional longitudinal behavioral genetic models estimate the relative contribution of genetic and environmental factors to stability and change of traits and behaviors. Longitudinal models rarely explain the processes that generate observed differences between genetically and socially related individuals. We propose that exchanges between individuals and their environments (i.e., phenotype-environment effects) can explain the emergence of observed differences over time. Phenotype-environment models, however, would require violation of the independence assumption of standard behavioral genetic models; that is, uncorrelated genetic and environmental factors. We review how specification of phenotype-environment effects contributes to understanding observed changes in genetic variability over time and longitudinal correlations among nonshared environmental factors. We then provide an example using 30 days of positive and negative affect scores from an all-female sample of twins. Results demonstrate that the phenotype-environment effects explain how heritability estimates fluctuate as well as how nonshared environmental factors persist over time. We discuss possible mechanisms underlying change in gene-environment correlation over time, the advantages and challenges of including gene-environment correlation in longitudinal twin models, and recommendations for future research.

On the etiology of internalizing and externalizing problem behavior: A twin-family study

Internalizing and externalizing behavior problems are established risk factors for many unpleasant outcomes and psychopathology in adulthood, and understanding the interplay between genes and environment is important for deducing implications for therapeutic interventions. Among genetic studies on internalizing and externalizing problem behavior, the heritability estimates differ widely. Most research only uses twin data and other-reports, and therefore certain limitations are inevitable. Our study is the first to investigate genetic and environmental influences on problem behavior using a Nuclear Twin Family Design and self-reports, in order to address these limitations. Internalizing and externalizing problem behavior of 3,087 twin pairs (age 11–23), a sibling, and their parents were analyzed with structural equation modeling to estimate heritability separately for each of three twin birth cohorts. Genetic influences account for about one-third of the variance for both internalizing and externalizing. Shared environmental influences were only found for internalizing, and through the advantages of considering data from the whole twin family, firstly could be identified as solely twin-specific. Our findings could contribute to a better understanding of the gap between heritability based on twin studies and DNA-based heritability (‘missing heritability problem’): Results indicate that heritability estimates gained via classic twin design and other-reports are slightly overestimated and therefore environmental influences, in general, are more important than previous research suggests. Simultaneously, we showed that family-specific environment either contributes to behavior problems only on an individual level, or that it has a lesser influence than originally thought.

Toddler risk and protective characteristics: Common and unique genetic and environmental influences

The goal of this study was to disentangle the common and unique genetic and environmental influences on social-emotional competence, problem behavior, physiological dysregulation, and negative emotionality (NE) in toddlers. The sample consisted of 243 twin pairs (mean age = 31.94 months) rated by primary caregivers (>95% mothers) on the Children's Behavior Questionnaire and the Infant-Toddler Social and Emotional Assessment. A multivariate Cholesky Decomposition revealed three shared environmental factors, with one set of environmental influences common to competence, problem behavior, and physiological dysregulation, a second common to problem behavior and physiological dysregulation, and a third common to physiological dysregulation and NE. Also, there were two additive genetic factors, with one explaining variance in competence, NE, and a small amount of variance in problem behavior, and a second explaining variance in problem behavior and NE. Given the common shared environmental factors across outcomes, these results suggest that toddlerhood could be a particularly important time to intervene, as interventions could simultaneously improve competencies and reduce problem behaviors. This study also highlights the need for genetically informed research to examine the etiology of multiple outcomes and address overlap.

Etiology of Stability and Growth of Internalizing and Externalizing Behavior Problems Across Childhood and Adolescence

Internalizing and externalizing behaviors are heritable, and show genetic stability during childhood and adolescence. Less work has explored how genes influence individual differences in developmental trajectories. We estimated ACE biometrical latent growth curve models for the Teacher Report Form (TRF) and parent Child Behavior Checklist (CBCL) internalizing and externalizing scales from ages 7 to 16 years in 408 twin pairs from the Colorado Longitudinal Twin Study. We found that Intercept factors were highly heritable for both internalizing and externalizing behaviors (a2 = .61-.92), with small and nonsignificant environmental influences for teacher-rated data but significant nonshared environmental influences for parent-rated data. There was some evidence of heritability of decline in internalizing behavior (Slopes for teacher and parent ratings), but the Slope genetic variance was almost entirely shared with that for the Intercept when different than zero. These results suggest that genetic effects on these developmental trajectories operate primarily on initial levels and stability, with no significant unique genetic influences for change. Finally, cross-rater analyses of the growth factor scores revealed moderate to large genetic and environmental associations between growth factors derived from parents' and teachers' ratings, particularly the Intercepts.

The Association of Intrapair Birth-Weight Differences With Internalizing and Externalizing Behavior Problems

Problem behaviors are of increasing public health concern. Twin studies have revealed substantial genetic and environmental influences on children's behavior, and examining birth-weight difference could allow the identification of the specific contribution of multiple non-shared prenatal environmental factors. The Twins and Multiple Births Association Heritability Study, a UK, volunteer-based study, recruited mothers of twins aged 18 months to 5 years; 960 twins (480 pairs) were included in the analysis. Twins' mothers answered questions relative to their pregnancy and their twins' characteristics, and completed the Child Behavior Checklist (CBCL) 1½-5. The association between the absolute birth-weight difference and each CBCL scale's score difference was analyzed by means of multiple linear regressions. Expected mean CBCL score differences were calculated. In monozygotic (MZ) twins, statistically and clinically significant associations were found between intrapair birth-weight difference and difference in total problems, internalizing problems, and emotional reactiveness. No significant results were observed neither in dizygotic (DZ) twins when analyzed as a separate group nor in MZ and DZ twins combined. The results of the present study suggest that with increasing the absolute birth-weight difference, the intrapair difference in total problems, internalizing behaviors and emotionality increases, with smaller twins being at major risk for later behavior problems. Moreover, these results suggest a causal association between birth weight and behavior development.

Familial and Special Twin Influences on Cigarette Use Initiation

BACKGROUND

Shared experiences within families play an important role in the initiation of cigarette use among adolescents. Behavioral genetic studies using various samples have implicated that the shared environment that twins experience is an important source of influence on whether adolescents initiate cigarette use. Whether the special twin environment, in addition to the shared environment, contributes significantly to making twin siblings more similar in cigarette initiation, and whether the influence of the special twin environment persists into adulthood, is less clear.

METHODS

Data for this study came from the National Longitudinal Survey of Adolescent Health. Twin, full-, and half-sibling pairs between the ages of 12 and 33 were separated into three age groups, with about 3,000 individuals in each age group. The proportion of variance in cigarette use initiation explained by genetic, shared, special twin, and unique environmental factors were examined.

RESULTS

The results of separate age-moderated univariate variance decomposition models indicate that the special twin environment does not significantly contribute to the variance in cigarette use initiation in adolescence or young adulthood.

CONCLUSION

Factors shared by individuals in a family, but that are not specific to being a twin, are important in determining whether adolescents will initiate the use of cigarettes.

Internalizing and externalizing problems in childhood and adolescence as predictors of work incapacity in young adulthood

BACKGROUND

There is limited information regarding the association between youth mental health problems and work incapacity in adulthood. We investigated whether internalizing (depressive, anxious, somatic complaints) and externalizing (aggressive, rule-breaking) behavior problems in childhood and adolescence were associated with sickness absence (SA) and disability pension (DP) in young adulthood.

METHODS

Data were used from the population-based and prospective Twin Study of Child and Adolescent Development (TCHAD) which includes all Swedish twins born in 1985-1986 (N = 2570). Internalizing and externalizing behavior problems were assessed with the Child Behavior Checklist at ages of 8-9, 13-14, 16-17, and 19-20 years. Individuals participating in TCHAD were followed regarding SA and DP during 2001-2013 using nationwide registers. Cox regression models were applied to assess hazard ratios (HR) with 95% confidence intervals (CI).

RESULTS

Each one-unit increase of rule-breaking behavior implied a significant higher risk for SA in early adulthood, despite of age at assessment, with the highest HR of 1.12 (95% CI 1.05-1.19) at age of 8-9 years. Higher levels of anxious and depressive symptoms in childhood and adolescence were associated with DP in early adulthood despite age at assessment, with the highest risk at age 19-20 years [HR 1.31 (95% CI 1.12-1.53)]. The associations attenuated slightly when familial factors were taken into account.

CONCLUSIONS

Internalizing and externalizing behavior problems identified at an early age (8-9 years) increased risk for SA and DP in young adulthood. These findings indicate that early prevention and intervention efforts to reduce behavior problems may promote a successful start in working life.

Callous-unemotional behaviors in early childhood: Genetic and environmental contributions to stability and change

Callous-unemotional (CU) behaviors demonstrate meaningful individual differences in early childhood, even in nonclinical samples with low mean levels of CU, but the factors underlying this variation have not been examined. This study investigated genetic and environmental contributions to individual differences and to sources of continuity and change in CU in toddler twins (145 monozygotic, 169 dizygotic) assessed at ages 2 and 3 years. CU, as assessed by the Child Behavior Checklist 1.5-5 (Achenbach & Rescorla, 2000), was moderately stable across age (r = .45, p < .0001). Longitudinal biometric analyses revealed genetic and nonshared environmental influences on CU at both ages, with no significant contribution from shared environmental factors. Stability from age 2 to 3 was due to genetic factors, whereas change was due to both genetic and nonshared environmental influences. This genetic and nonshared environmental change was substantial, suggesting malleability of CU in early childhood. Over 50% of the genetic influences and 100% of the nonshared environmental influences on CU at age 3 were independent of those that operated at age 2. Implications of novel sources of variance across age are discussed.

Developmental changes in genetic and environmental influences on Chinese child and adolescent anxiety and depression

BACKGROUND

Twin and family studies using Western samples have established that child and adolescent anxiety and depression are under substantial genetic, modest shared environmental, and substantial non-shared environmental influences. Generalizability of these findings to non-Western societies remains largely unknown, particularly regarding the changes of genetic and environmental influences with age. The current study examined changes in genetic and environmental influences on self-reported anxiety and depression from late childhood to mid-adolescence among a Chinese twin sample. Sex differences were also examined.

METHOD

Self-reported anxiety and depression were collected from 712 10- to 12-year-old Chinese twins (mean = 10.88 years, 49% males) and again 3 years later. Quantitative genetic modeling was used to examine developmental changes in genetic and environmental influences on anxiety and depression, and sex differences.

RESULTS

Heritability of anxiety and depression in late childhood (23 and 20%) decreased to negligible in mid-adolescence, while shared environmental influences increased (20 and 27% to 57 and 60%). Shared environmental factors explained most of the continuity of anxiety and depression (75 and 77%). Non-shared environmental factors were largely time-specific. No sex differences were observed.

CONCLUSIONS

Shared environmental influences might be more pronounced during the transition period of adolescence in non-Western societies such as China. Future research should examine similarities and differences in the genetic and environmental etiologies of child and adolescent internalizing and other psychopathology in development between Western and non-Western societies.

Aetiological influences on stability and change in emotional and behavioural problems across development: a systematic review

Emotional and behavioural problems in childhood and adolescence can be chronic and are predictive of future psychiatric problems. Understanding what factors drive the development and maintenance of these problems is therefore crucial. Longitudinal behavioural genetic studies using twin, sibling or adoption data can be used to explore the developmental aetiology of stability and change in childhood and adolescent psychopathology. We present a systematic review of longitudinal, behavioural genetic analyses of emotional and behavioural problems between ages 0 to 18 years. We identified 58 studies, of which 19 examined emotional problems, 30 examined behavioural problems, and 9 examined both. In the majority of studies, stability in emotional and behavioural problems was primarily genetically influenced. Stable environmental factors were also widely found, although these typically played a smaller role. Both genetic and environmental factors were involved in change across development. We discuss the findings in the context of the wider developmental literature and make recommendations for future research.

Testing Causal Effects of Maternal Smoking During Pregnancy on Offspring's Externalizing and Internalizing Behavior

Maternal smoking during pregnancy (SDP) is associated with increased risk of externalizing and internalizing behaviors in offspring. Two explanations (not mutually exclusive) for this association are direct causal effects of maternal SDP and the effects of genetic and environmental factors common to parents and offspring which increase smoking as well as problem behaviors. Here, we examined the associations between parental SDP and mother rated offspring externalizing and internalizing behaviors (rated by the Child Behavior Checklist/2-3) at age three in a population-based sample of Dutch twins (N = 15,228 pairs). First, as a greater effect of maternal than of paternal SDP is consistent with a causal effect of maternal SDP, we compared the effects of maternal and paternal SDP. Second, as a beneficial effect of quitting smoking before pregnancy is consistent with the causal effect, we compared the effects of SDP in mothers who quit smoking before pregnancy, and mothers who continued to smoke during pregnancy. All mothers were established smokers before their pregnancy. The results indicated a greater effect of maternal SDP, compared to paternal SDP, for externalizing, aggression, overactive and withdrawn behavior. Quitting smoking was associated with less externalizing, overactive behavior, aggression, and oppositional behavior, but had no effect on internalizing, anxious depression, or withdrawn behavior. We conclude that these results are consistent with a causal, but small, effect of smoking on externalizing problems at age 3. The results do not support a causal effect of maternal SDP on internalizing behaviors.

The stability and change of etiological influences on depression, anxiety symptoms and their co-occurrence across adolescence and young adulthood

BACKGROUND

Depression and anxiety persist within and across diagnostic boundaries. The manner in which common v. disorder-specific genetic and environmental influences operate across development to maintain internalizing disorders and their co-morbidity is unclear. This paper investigates the stability and change of etiological influences on depression, panic, generalized, separation and social anxiety symptoms, and their co-occurrence, across adolescence and young adulthood.

METHOD

A total of 2619 twins/siblings prospectively reported symptoms of depression and anxiety at mean ages 15, 17 and 20 years.

RESULTS

Each symptom scale showed a similar pattern of moderate continuity across development, largely underpinned by genetic stability. New genetic influences contributing to change in the developmental course of the symptoms emerged at each time point. All symptom scales correlated moderately with one another over time. Genetic influences, both stable and time-specific, overlapped considerably between the scales. Non-shared environmental influences were largely time- and symptom-specific, but some contributed moderately to the stability of depression and anxiety symptom scales. These stable, longitudinal environmental influences were highly correlated between the symptoms.

CONCLUSIONS

The results highlight both stable and dynamic etiology of depression and anxiety symptom scales. They provide preliminary evidence that stable as well as newly emerging genes contribute to the co-morbidity between depression and anxiety across adolescence and young adulthood. Conversely, environmental influences are largely time-specific and contribute to change in symptoms over time. The results inform molecular genetics research and transdiagnostic treatment and prevention approaches.

Top 10 Replicated Findings From Behavioral Genetics

In the context of current concerns about replication in psychological science, we describe 10 findings from behavioral genetic research that have replicated robustly. These are "big" findings, both in terms of effect size and potential impact on psychological science, such as linearly increasing heritability of intelligence from infancy (20%) through adulthood (60%). Four of our top 10 findings involve the environment, discoveries that could have been found only with genetically sensitive research designs. We also consider reasons specific to behavioral genetics that might explain why these findings replicate.

Differential genetic and environmental influences on developmental trajectories of antisocial behavior from adolescence to young adulthood

Little research has investigated differential genetic and environmental influences on different developmental trajectories of antisocial behavior. This study examined genetic and environmental influences on liabilities of being in life-course-persistent (LCP) and adolescent-limited (AL) type delinquent groups from adolescence to young adulthood while considering nonviolent and violent delinquency subtypes and gender differences. A genetically informative sample (n = 356, 15-16 years) from the first three waves of In-Home Interview of the National Longitudinal Study of Adolescent to Adult Health was used, with 94 monozygotic and 84 dizygotic pairs of same-sex twins (50% male). Biometric liability threshold models were fit and found that the male-specific LCP type class, chronic, showed more genetic influences, while the AL type classes, decliner and desister, showed more environmental influences. Genetic liability and shared environment both influence the persistence of antisocial behavior. The development of female antisocial behavior appears to be influenced more by shared environment.

Chorionicity and Heritability Estimates from Twin Studies: The Prenatal Environment of Twins and Their Resemblance Across a Large Number of Traits

There are three types of monozygotic (MZ) twins. MZ twins can either share one chorion and one amnion, each twin can have its own amnion, or MZ twins can—like dizygotic twins—each have their own chorion and amnion. Sharing the same chorion may create a more similar/dissimilar prenatal environment and bias heritability estimates, but most twin studies do not distinguish between these three types of MZ twin pairs. The aim of this paper is to investigate the effect of chorion sharing on the similarity within MZ twin pairs for a large number of traits. Information on chorion status was obtained for the Netherlands twin register (NTR) by linkage to the records from the database of the dutch pathological anatomy national automated archive (PALGA). Record linkage was successful for over 9000 pairs. Effect of chorion type was tested by comparing the within-pair similarity between monochorionic (MC) and dichorionic (DC) MZ twins on 66 traits including weight, height, motor milestones, child problem behaviors, cognitive function, wellbeing and personality. For only 10 traits, within-pair similarity differed between MCMZ and DCMZ pairs. For traits influenced by birth weight (e.g. weight and height in young children) we expected that MC twins would be more discordant. This was found for 5 out of 13 measures. When looking at traits where blood supply is important, we saw MCMZ twins to be more concordant than DCMZ’s for 3 traits. We conclude that the influence on the MZ twin correlation of the intra-uterine prenatal environment, as measured by sharing a chorion type, is small and limited to a few phenotypes. This implies that the assumption of equal prenatal environment of mono- and DC MZ twins, which characterizes the classical twin design, is largely tenable.

Single Nucleotide Polymorphism Heritability of Behavior Problems in Childhood: Genome-Wide Complex Trait Analysis

OBJECTIVE

Genetic factors contribute to individual differences in behavior problems. In children, genome-wide association studies (GWAS) have yielded the first suggestive results when aiming to identify genetic variants that explain heritability, but the proportion of genetic variance that can be attributed to common single nucleotide polymorphisms (SNPs) remains to be determined, as only a few studies have estimated SNP heritability, with diverging results.

METHOD

Genomic-relationship-matrix restricted maximum likelihood (GREML) as implemented in the software Genome-Wide Complex Trait Analysis (GCTA) was used to estimate SNP heritability (SNP h(2)) for multiple phenotypes within 4 broad domains of children's behavioral problems (attention-deficit/hyperactivity symptoms, internalizing, externalizing, and pervasive developmental problems) and cognitive function. We combined phenotype and genotype data from 2 independent, population-based Dutch cohorts, yielding a total number of 1,495 to 3,175 of 3-, 7-, and 9-year-old children.

RESULTS

Significant SNP heritability estimates were found for attention-deficit/hyperactivity symptoms (SNP h(2) = 0.37-0.71), externalizing problems (SNP h(2) = 0.44), and total problems (SNP h(2) = 0.18), rated by mother or teacher. Sensitivity analyses with exclusion of extreme cases and quantile normalization of the phenotype data decreased SNP h(2) as expected under genetic inheritance, but they remained statistically significant for most phenotypes.

CONCLUSION

We provide evidence of the influence of common SNPs on child behavior problems in an ethnically homogenous sample. These results support the continuation of large GWAS collaborative efforts to unravel the genetic basis of complex child behaviors.

Self-regulatory failure and the perpetration of adolescent dating violence: Examining an alcohol use by gene explanation

Studies report that alcohol use is related to partner violence, but for many, alcohol use does not culminate in violence against partners. Guided by a self-regulatory failure framework, we predicted that alcohol use would be more strongly associated with dating violence perpetration among adolescents with genotypes linked to impulsivity and emotional reactivity. The hypothesis was tested using random coefficient modeling of data from a multi-wave longitudinal study spanning grades 8-12 (ages 13-18) (n = 1,475). Analyses adjusted for multiple testing and race, and the potential for gene by environment correlation was examined. As predicted, alcohol use was more strongly associated with dating violence among adolescents who had a high rather than a low multilocus genetic profile composed of five genetic markers that influence dopamine signaling. Alcohol use was more strongly related to dating violence among boys with long rather than short 5-HTTLPR alleles, the opposite of the prediction. MAOA-uVNTR did not interact with alcohol, but it had a main effect on dating violence by boys in later grades in the expected direction: boys with more low activity alleles perpetrated more dating violence. Exploratory analyses found variation in findings by race. Our findings demonstrate the importance of incorporating genes into etiological studies of adolescent dating violence, which to date has not been done. Aggr. Behav. Aggr. Behav. 42:189-203, 2015. © 2014 Wiley Periodicals, Inc.

Maternal pre-pregnancy weight and externalising behaviour problems in preschool children: a UK-based twin study

OBJECTIVE

To estimate the heritability of child behaviour problems and investigate the association between maternal pre-pregnancy overweight and child behaviour problems in a genetically sensitive design.

DESIGN

Observational cross-sectional study.

SETTING

The Twins and Multiple Births Association Heritability Study (TAMBAHS) is an online UK-wide volunteer-based study investigating the development of twins from birth until 5 years of age.

PARTICIPANTS

A total of 443 (16% of the initial registered members) mothers answered questions on pre-pregnancy weight and their twins' internalising and externalising problems using the Child Behavior Checklist and correcting for important covariates including gestational age, twins' birth weight, age and sex, mother's educational level and smoking (before, during and after pregnancy).

PRIMARY OUTCOMES

The heritability of behaviour problems and their association with maternal pre-pregnancy weight.

RESULTS

The genetic analysis suggested that genetic and common environmental factors account for most of the variation in externalising disorders (an ACE model was the most parsimonious with genetic factors (A) explaining 46% (95% CI 33% to 60%) of the variance, common environment (C) explaining 42% (95% CI 27% to 54%) and non-shared environmental factors (E) explaining 13% (95% CI 10% to 16%) of the variance. For internalising problems, a CE model was the most parsimonious model with the common environment explaining 51% (95% CI 44% to 58%) of the variance and non-shared environment explaining 49% (95% CI 42% to 56%) of the variance. Moreover, the regression analysis results suggested that children of overweight mothers showed a trend (OR=1.10, 95% CI 0.58% to 2.06) towards being more aggressive and exhibit externalising behaviours compared to children of normal weight mothers.

CONCLUSIONS

Maternal pre-pregnancy weight may play a role in children's aggressive behaviour.

Do non-shared environmental influences persist over time? An examination of days and minutes

Non-shared environmental influences show only minimal stability over time prior to adulthood. The long assessment lags (typically 3-5 years) that characterize most longitudinal twin studies, however, make it difficult to interpret these results. To more rigorously evaluate non-shared environmental stability prior to adulthood, we fitted biometric correlated factors models to (1) seven consecutive days of self-reported negative and positive affect in 239 twin pairs aged 16-25 years and (2) seven consecutive minutes of observer rated warmth and control in 687 twin pairs aged 6-10 years. We then empirically examined patterns of etiologic stability over time using a mixed effects analog to the one-way ANOVA. Genetic and shared environmental correlations were found to be highly stable over both days and minutes. By contrast, non-shared environmental correlations decreased monotonically with increasing lag length, and moreover, were small-to moderate in magnitude when examining intervals longer than a few minutes. Such findings imply that the non-shared environment may be comprised primarily of transient and idiosyncratic effects prior to adulthood.

Identical genetic influences underpin behavior problems in adolescence and basic traits of personality

BACKGROUND

Understanding the etiology of adolescent problem behavior has been of enduring interest. Only relatively recently, however, has this issue been examined within a normal personality trait framework. Research suggests that problem behaviors in adolescence and beyond may be adequately explained by the taxonomy provided by the basic dimensions of normal personality: Such problem behaviors are suggested to be extreme points on a distribution of the full range of the underlying traits. We extend work in this field examining the extent to which genetic factors underlying the five-factor model of personality are common with genetic influences on adolescent behavior problems (namely, anxiety, peer problems, conduct, hyperactivity, and low prosociality).

METHOD

A nationally representative twin sample (Twins Early Development Study) from the general population of England and Wales, including 2031 pairs of twins aged 16 years old, was used to decompose variation into genetic and environmental components. Behavioral problems in adolescence were assessed by self-report with the Strengths and Difficulties Questionnaire.

RESULTS

Adolescent behavior problems were moderately associated with normal personality: Specifically, a fifth to a third of phenotypic variance in problem behaviors was accounted for by five-factor model personality traits. Of central importance here, genetic influences underpinning personality were entirely overlapping with those genetic factors underlying adolescent behavior problems.

CONCLUSIONS

These findings suggest that adolescent behavior problems can be understood, at least in part, within a model of normal personality trait variation, with the genetic bases of these behavior problems the same as those genetic influences underpinning normal personality.

A genome-wide association meta-analysis of preschool internalizing problems

OBJECTIVE

Preschool internalizing problems (INT) are highly heritable and moderately genetically stable from childhood into adulthood. Gene-finding studies are scarce. In this study, the influence of genome-wide measured single nucleotide polymorphisms (SNPs) was investigated in 3 cohorts (total N = 4,596 children) in which INT was assessed with the same instrument, the Child Behavior Checklist (CBCL).

METHOD

First, genome-wide association (GWA) results were used for density estimation and genome-wide complex trait analysis (GCTA) to calculate the variance explained by all SNPs. Next, a fixed-effect inverse variance meta-analysis of the 3 GWA analyses was carried out. Finally, the overlap in results with prior GWA studies of childhood and adulthood psychiatric disorders and treatment responses was tested by examining whether SNPs associated with these traits jointly showed a significant signal for INT.

RESULTS

Genome-wide SNPs explained 13% to 43% of the total variance. This indicates that the genetic architecture of INT mirrors the polygenic model underlying adult psychiatric traits. The meta-analysis did not yield a genome-wide significant signal but was suggestive for the PCSK2 gene located on chromosome 20p12.1. SNPs associated with other psychiatric disorders appeared to be enriched for signals with INT (λ = 1.26, p < .03).

CONCLUSION

Our study provides evidence that INT is influenced by many common genetic variants, each with a very small effect, and that, even as early as age 3, genetic variants influencing INT overlap with variants that play a role in childhood and adulthood psychiatric disorders.

Child care, socio-economic status and problem behavior: a study of gene-environment interaction in young Dutch twins

The influences of formal child care before age 4 on behavioral problems at 3, 5, and 7 years of age were assessed in 18,932 Dutch twins (3,878 attended formal child care). The effect of formal child care was studied on the average level of problem behavior and as moderator of genetic and non-genetic influences, while taking into account effects of sex and parental socio-economic status (SES). There was a small association between attending formal child care and higher externalizing problems, especially when SES was low. Heritability was lower for formal child care and in lower SES conditions. These effects were largest at age 7 and for externalizing problems. In 7 year-old boys and girls, the difference in heritability between the formal child care group of low SES and the home care group of high SES was 30% for externalizing and ~20% for internalizing problems. The decrease in heritability was explained by a larger influence of the environment, rather than by a decrease in genetic variance. These results support a bioecological model in which heritability is lower in circumstances associated with more problem behavior.

GE covariance through phenotype to environment transmission: an assessment in longitudinal twin data and application to childhood anxiety

We considered identification of phenotype (at occasion t) to environment (at occasion t + 1) transmission in longitudinal model comprising genetic, common and unique environmental simplex models (autoregressions). This type of transmission, which gives rise to genotype-environment covariance, is considered to be important in developmental psychology. Having established identifying constraints, we addressed the issue of statistical power to detect such transmission given a limited set of parameter values. The power is very poor in the ACE simplex, but is good in the AE model. We investigated misspecification, and found that fitting the standard ACE simplex to covariance matrices generated by an AE simplex with phenotype to E transmission produces the particular result of a rank 1 C (common environment) covariance matrix with positive transmission, and a rank 1 D (dominance) matrix given negative transmission. We applied the models to mother ratings of anxiety in female twins (aged 3, 7, 10, and 12 years), and obtained support for the positive effect of one twin's phenotype on the other twin's environment.

Research review: the shared environment as a key source of variability in child and adolescent psychopathology

BACKGROUND

Behavioral genetic research has historically concluded that the more important environmental influences were nonshared or result in differences between siblings, whereas environmental influences that create similarities between siblings (referred to as shared environmental influences) were indistinguishable from zero. Recent theoretical and meta-analytic work {Burt. Psychological Bulletin [135 (2009) 608]} has challenged this conclusion as it relates to child and adolescent psychopathology, however, arguing that the shared environment is a moderate, persistent, and identifiable source of individual differences in such outcomes prior to adulthood.

METHODS

The current review seeks to bolster research on the shared environment by highlighting both the logistic advantages inherent in studies of the shared environment, as well as the use of nontraditional but still genetically informed research designs to study shared environmental influences.

RESULTS

Although often moderate in magnitude prior to adulthood and free of unsystematic measurement error, shared environmental influences are nevertheless likely to have been underestimated in prior research. Moreover, the shared environment is likely to include proximal effects of the family, as well as the effects of more distal environmental contexts such as neighborhood and school. These risk and protective factors could influence the child either as main effects or as moderators of genetic influence (i.e. gene-environment interactions). Finally, because the absence of genetic relatedness in an otherwise nonindependent dataset also qualifies as 'genetically informed', studies of the shared environment are amenable to the use of novel and non-traditional designs (with appropriate controls for selection).

CONCLUSIONS

The shared environment makes important contributions to most forms of child and adolescent psychopathology. Empirical examinations of the shared environment would thus be of real and critical value for understanding the development and persistence of common mental health issues prior to adulthood.

Chronic bullying victimization across school transitions: the role of genetic and environmental influences

We investigated the antecedents and consequences of chronic victimization by bullies across a school transition using a genetically sensitive longitudinal design. Data were from the Environmental Risk Longitudinal Twin Study (E-Risk), an epidemiological cohort of 2,232 children. We used mothers' and children's reports of bullying victimization during primary school and early secondary school. Children who experienced frequent victimization at both time points were classed as "chronic victims" and were found to have an increased risk for mental health problems and academic difficulties compared to children who were bullied only in primary school, children bullied for the first time in secondary school, and never-bullied children. Biometric analyses revealed that stability in victimization over this period was influenced primarily by genetic and shared environmental factors. Regression analyses showed that children's early characteristics such as preexistent adjustment difficulties and IQ predicted chronic versus transitory victimization. Family risk factors for chronic victimization included socioeconomic disadvantage, low maternal warmth, and maltreatment. Our results suggest that bullying intervention programs should consider the role of the victims' behaviors and family background in increasing vulnerability to chronic victimization. Our study highlights the importance of widening antibullying interventions to include families to reduce the likelihood of children entering a pathway toward chronic victimization.

Phenotype-environment correlations in longitudinal twin models

Gene-environment correlation (rGE) exists both within and between families. Between families, accumulating rGE has been used to explain dramatic changes in phenotypic means over time. The Dickens and Flynn model of increases in cognitive ability over generational time, for example, suggests that small changes in phenotype can lead to subsequent reallocation of environmental resources. This process sets up a reciprocal feedback loop between phenotype and environment, producing accumulating rGE that can cause large changes in the mean of ability, even though ability remains highly heritable in cross-sectional data. We report simulations suggesting that similar processes may operate within twin and sibling pairs. Especially in dizygotic twins and siblings, small differences in phenotype can become associated with reallocations of environmental resources within families. We show that phenotype-environment effects can account for age-related increases in rGE, rapid differentiation of siblings raised together, and widely reported increases in the heritability of behavior during childhood and adolescence.

Biology, genes, and resilience: toward a multidisciplinary approach

Variability in response to stressful environmental exposures is at the core of resilience research. In order to understand why some individuals show resilient functioning in the face of adversity, one needs to understand the mechanisms through which risky environments lead to pathology in some and not others, and the ways in which risk and protective factors affect these processes. Understanding the interplay between genetic and biological processes and different environments is necessary in order to elucidate the causal pathways through which individuals show resilience or vulnerability in the face of adversity.

Exploring the association between well-being and psychopathology in adolescents

Promotion of mental well-being and prevention of emotional and behavioral problems are suggested to go hand in hand. The present study examined the association between subjective well-being (SWB) and psychopathology and investigated the etiology of this association in a large population-based cohort study of adolescent twins (n = 9,136) and their non-twin siblings (n = 1,474) aged 12–20 years. Phenotypic, genetic, and environmental correlations between SWB and psychopathology were obtained from multivariate genetic modeling conditional on sex. An SWB factor score was used based on measures of subjective happiness, satisfaction with life, and quality of life. Psychopathology was obtained from all syndrome and broad-band scales of the Dutch version of the ASEBA Youth Self Report. Males reported significantly higher levels of SWB than females. Females reported significantly more internalizing problems while males report significantly higher levels of externalizing behavior. In both sexes, significant negative associations were found between SWB and psychopathology, with the strongest associations seen for SWB and the YSR syndrome scale anxious/depression behavior. The observed associations were primarily explained by genetic correlations while non-shared environmental influences were mainly domain specific. The genetic liability to lower levels of SWB are indicative of a genetic liability to higher levels of psychopathology, suggesting that it might be feasible to screen for emotional and behavioral problems before clear signs are present by screening on indices of subjective well-being.

Genetic innovation and stability in externalizing problem behavior across development: a multi-informant twin study

The use of cross-informant ratings in previous longitudinal studies on externalizing behavior may have obscured the presence of continuity of genetic risk. The current study included latent factors representing the latent estimates of externalizing behavior based on both parent and self-report which eliminated rater-specific effects from these latent estimates. Symptoms of externalizing behavior of 1,480 Swedish twin pairs were obtained at ages 8-9, 13-14, 16-17 and 19-20 both by parent and self-report. Mx modeling was used to estimate additive genetic, shared and specific environmental influences. Genetic continuity was found over the entire developmental period as well as additional sources of genetic influence emerging around early and late adolescence. New unique environmental effects (E) on externalizing behavior arose early in adolescence. The results support both the presence of genetic continuity and change in externalizing behavior during adolescence due to newly emerging genetic and environmental risk factors.

Gene-environment interaction in teacher-rated internalizing and externalizing problem behavior in 7- to 12-year-old twins

BACKGROUND

Internalizing and externalizing problem behavior at school can have major consequences for a child and is predictive for disorders later in life. Teacher ratings are important to assess internalizing and externalizing problems at school. Genetic epidemiological studies on teacher-rated problem behavior are relatively scarce and the reported heritability estimates differ widely. A unique feature of teacher ratings of twins is that some pairs are rated by different and others are rated by the same teacher. This offers the opportunity to assess gene-environment interaction.

METHODS

Teacher ratings of 3,502 7-year-old, 3,134 10-year-old and 2,193 12-year-old twin pairs were analyzed with structural equation modeling. About 60% of the twin pairs were rated by the same teacher. Twin correlations and the heritability of internalizing and externalizing behavior were estimated, separately for pairs rated by the same and different teachers. Socioeconomic status and externalizing behavior at age 3 were included as covariates.

RESULTS

Twin correlations and heritability estimates were higher when twin pairs were in the same class and rated by the same teacher than when pairs were rated by different teachers. These differences could not be explained by twin confusion or rater bias. When twins were rated by the same teacher, heritability estimates were about 70% for internalizing problems and around 80% in boys and 70% in girls for externalizing problems. When twins were rated by different teachers, heritability estimates for internalizing problems were around 30% and for externalizing problems around 50%.

CONCLUSIONS

Exposure to different teachers during childhood may affect the heritability of internalizing and externalizing behavior at school. This finding points to gene-environment interaction and is important for the understanding of childhood problem behavior. In addition, it could imply an opportunity for interventions at school.

Parent-child interaction therapy for preschool children with disruptive behaviour problems in the Netherlands

BACKGROUND

Persistent high levels of aggressive, oppositional and impulsive behaviours, in the early lives of children, are significant risk factors for adolescent and adult antisocial behaviour and criminal activity. If the disruptive behavioural problems of young children could be prevented or significantly reduced at an early age, the trajectory of these behavioural problems leading to adolescent delinquency and adult antisocial behaviour could be corrected. Parent-Child Interaction Therapy (PCIT) is a short-term, evidence-based, training intervention for parents dealing with preschool children, who exhibit behavioural problems. Recently, PCIT was implemented in a Dutch community mental health setting. This present study aims to examine the short-term effects of PCIT on reducing the frequency of disruptive behaviour in young children.

METHODS

This study is based on the data of 37 referred families. Whereby the results of which are derived from an analysis of parent reports of the Eyberg Child Behavior Inventory (ECBI), obtained during each therapeutic session. Furthermore, demographic information, extracted from client files, was also utilized. However, it must be noted that eleven families (27.5%) dropped out of treatment before the treatment protocol was completed. To investigate the development of disruptive behaviour, a non-clinical comparison group was recruited from primary schools (N = 59).

RESULTS

The results of this study indicate that PCIT significantly reduces disruptive behaviour in children. Large effect sizes were found for both fathers and mothers reported problems (d = 1.88, d = 1.99, respectively), which is similar to American outcome studies. At post treatment, no differences were found concerning the frequency of behavioural problems of children who completed treatment and those who participated in the non-clinical comparison group.

CONCLUSION

The findings of this study suggest that PCIT is potentially an effective intervention strategy for young children and their parents in the Dutch population. However, further research into the evaluation of PCIT using a randomised controlled trial is recommendable.

Additional evidence against shared environmental contributions to attention-deficit/hyperactivity problems

A recent meta-analysis "Burt (Psychol Bull 135:608-637, 2009)" indicated that shared environmental influences (C) do not contribute to Attention-Deficit/Hyperactivity Disorder (ADHD). Unfortunately, the meta-analysis relied almost exclusively on classical twin studies. Although useful in many ways, some of the assumptions of the classical twin model (e.g., dominant genetic and shared environmental influences do not simultaneously influence the phenotype) can artifactually decrease estimates of C. There is thus a need to confirm that dominant genetic influences are not suppressing estimates of C on ADHD. The current study sought to do just this via the use of a nuclear twin family model, which allows researchers to simultaneously model and estimate dominant genetic and shared environmental influences. We examined two independent samples of child twins: 312 pairs from the Michigan State University Twin Registry and 854 pairs from the PrE School Twin Study in Sweden. Shared environmental influences were found to be statistically indistinguishable from zero and to account for less than 5 % of the variance. We conclude that the presence of dominant genetic influences does not account for the absence of C on ADHD.

Association of childhood family environments with the risk of social withdrawal ('hikikomori') in the community population in Japan

AIMS

Hikikomori is a form of social withdrawal among those who retreat from social interaction for protracted periods of time. This study examines family-related childhood factors for hikikomori using the retrospective data derived from a population-based survey.

METHODS

We derived data from World Mental Health Survey Japan. The subjects of this study were community residents aged 20-49 years (n=708). Multiple logistic regression was applied to examine the association between the lifetime experience of hikikomori and childhood family environment, adjusting for sex, age, and respondents' history of common mental disorders.

RESULTS

Father's high educational level (odds ratio [OR]=6.0, 95% confidence interval [CI]=1.6-22.9), mother's common mental disorders (OR=5.9, 95%CI=1.1-33.3), and mother's panic disorders (OR=6.6, 95%CI=1.1-39.1) were significantly and positively associated with hikikomori after controlling for respondents' sex, age, and history of mental disorders.

CONCLUSIONS

Our findings suggest that hikikomori cases are more likely to occur in families where the parents have high levels of education. Maternal panic disorder may be another risk factor for children to develop hikikomori.

Genetic Influences on Thought Problems in 7-Year-Olds: A Twin-Study of Genetic, Environmental and Rater Effects

The Thought–Problem scale (TP) of the CBCL assesses symptoms such as hallucinations and strange thoughts/behaviors and has been associated with other behavioral disorders. This study uses parental reports to examine the etiology of variation in TP, about which relatively little is known, in 7-year-old twins. Parental ratings on TP were collected in 8,962 7-year-old twin pairs. Because the distribution of TP scores was highly skewed scores were categorized into 3 classes. The data were analyzed under a threshold liability model with genetic structural equation modeling. Ratings from both parents were simultaneously analyzed to determine the rater agreement phenotype (or common phenotype [TPc]) and the rater specific phenotype [TPs] that represents rater disagreement caused by rater bias, measurement error and/or a unique view of the parents on the child's behavior. Scores on the TP-scale varied as a function of rater (fathers rated fewer problems), sex (boys scored higher) and zygosity (DZ twins scored higher). The TPc explained 67% of the total variance in the parental ratings. Variation in TPc was influenced mainly by the children's genotype (76%). Variance in TPs also showed a contribution of genetic factors (maternal reports: 61%, paternal reports: 65%), indicating that TPs does not only represent rater bias. Shared environmental influences were only found in the TPs. No sex differences in genetic architecture were observed. These results indicate an important contribution of genetic factors to thought problems in children as young as 7 years.

Genetic Analyses of Teacher Ratings of Problem Behavior in 5-Year-Old Twins

Behavioral problems in young children can be assessed by asking their parents or teachers to rate their behaviors. Genetic analyses of parental ratings show relatively large heritabilities for emotional and behavioral problems in young children, but data from teachers for this age group are scarce. Sources of variation in the Teacher's Report Form (TRF) problem scales were examined. The TRF was completed for 211 Dutch 5-year-old twin pairs and 4 single twins. Twins rated by different teachers had higher means and variances than twins rated by the same teacher, in addition twin correlations were lower in this group. In both groups monozygotic (MZ) correlations were generally higher than dizygotic (DZ) correlations. A model for twin resemblance was tested that allowed for these effects. For 5 problem scales (Withdrawn, Social Problems, Aggressive Behavior, Rule Breaking Behavior and Attention Problems) a model with genetic and unique environmental sources of variation fitted best to the data. For 3 problem scales (Anxious/Depressed, Thought Problems and Somatic Complaints) there were familial influences but it was not possible to distinguish between common environmental influences or genetic influences. Heritability was 63% for Attention problems, around 45% for Withdrawn, Social Problems, Aggressive Behavior and Rule Breaking Behavior, and around 30% for Anxious/Depressed, Thought Problems and Somatic Complaints.

Longitudinal Genetic Analysis of Internalizing and Externalizing Problem Behavior in Adopted Biologically Related and Unrelated Sibling Pairs

To obtain a better understanding of how genetic and environmental processes are involved in the stability and change in problem behavior from early adolescence into adulthood, studies with genetically informative samples are important. The present study used parent-reported data on internalizing and externalizing problem behavior of adoptees at mean ages 12.4, 15.5 and 26.3. In this adoption study adopted biologically related sibling pairs shared on average 50% of their genes and were brought up in the same family environment, whereas adopted biologically unrelated sibling pairs only shared their family environment. The resemblance between these adopted biologically related (N = 106) and unrelated sibling pairs (N = 230) was compared and examined over time. We aimed to investigate (1) to what extent are internalizing and externalizing problem behavior stable from early adolescence into adulthood, and (2) whether the same or different genetic and environmental factors affect these problem behaviors at the 3 assessments. Our results show that both internalizing (rs ranging from .34 to .58) and externalizing behavior (rs ranging from .47 to .69) were rather stable over time. For internalizing and externalizing problem behavior it was found that both genetic and shared environmental influences could be modeled by an underlying common factor, which explained variance in problem behavior from early adolescence into adulthood and accounted for stability over time. The nonshared environmental influences were best modeled by a Cholesky decomposition for internalizing behavior, whereas a time-specific influence of the nonshared environment was included in the final model of externalizing behavior.

The Australian Twin ADHD Project: Current Status and Future Directions

This article describes the Australian Twin Attention-deficit/hyperactivity disorder (ADHD) Project (ATAP), the results of research conducted using this database and plans for future studies. Information has been actively collected from Australian families with twin children since 1991 for the ATAP database. The value of assessing siblings as well as twins is emphasized. Much work has gone into continuing the involvement of families in the study though this does become more difficult when twins reach maturity. The main focus of the project is ADHD in children and adolescents plus comorbid conditions including conduct disorder, oppositional defiant disorder, and generalized anxiety disorder. A major challenge has been how to retain continuity in the assessments, while at the same time covering changes in psychiatric classification, such as the move to Diagnostic and Statistical Manual of Mental Disorders (4th ed.; DSM-IV; American Psychiatric Association, 1994). Changes in the scale can affect the reports of twin similarity. Over the years, these twins have become part of other twin studies and future plans include linking different twin databases to investigate the relationships between childhood behavior and adult conditions. Recruitment, assessment and retention of twin families require a major commitment but create a significant resource for collaboration in areas outside the original aim.

Childhood problem behavior and parental divorce: evidence for gene-environment interaction

OBJECTIVE

The importance of genetic and environmental influences on children's behavioral and emotional problems may vary as a function of environmental exposure. We previously reported that 12-year-olds with divorced parents showed more internalizing and externalizing problems than children with married parents, and that externalizing problems in girls precede and predict later parental divorce. The aim of the current study was to investigate as to whether genetic and environmental influences on internalizing and externalizing problems were different for children from divorced versus non-divorced families.

METHODS

Maternal ratings on internalizing and externalizing problems were collected with the Child Behavior Checklist in 4,592 twin pairs at ages 3 and 12 years, of whom 367 pairs had experienced a parental divorce between these ages. Variance in internalizing and externalizing problems at ages 3 and 12 was analyzed with biometric models in which additive genetic and environmental effects were allowed to depend on parental divorce and sex. A difference in the contribution of genetic and environmental influences between divorced and non-divorced groups would constitute evidence for gene-environment interaction.

RESULTS

For both pre- and post-divorce internalizing and externalizing problems, the total variances were larger for children from divorced families, which was mainly due to higher environmental variances. As a consequence, heritabilities were lower for children from divorced families, and the relative contributions of environmental influences were higher.

CONCLUSIONS

Environmental influences become more important in explaining variation in children's problem behaviors in the context of parental divorce.

Are autistic traits in the general population stable across development?

There is accumulating evidence that autistic traits (AT) are on a continuum in the general population, with clinical autism representing the extreme end of a quantitative distribution. While the nature and severity of symptoms in clinical autism are known to persist over time, no study has examined the long-term stability of AT among typically developing toddlers. The current investigation measured AT in 360 males and 400 males from the general population close to two decades apart, using the Pervasive Developmental Disorder subscale of the Child Behavior Checklist in early childhood (M = 2.14 years; SD = 0.15), and the Autism-Spectrum Quotient in early adulthood (M = 19.50 years; SD = 0.70). Items from each scale were further divided into social (difficulties with social interaction and communication) and non-social (restricted and repetitive behaviours and interests) AT. The association between child and adult measurements of AT as well the influence of potentially confounding sociodemographic, antenatal and obstetric variables were assessed using Pearson's correlations and linear regression. For males, Total AT in early childhood were positively correlated with total AT (r = .16, p = .002) and social AT (r = .16, p = .002) in adulthood. There was also a positive correlation for males between social AT measured in early childhood and Total (r = .17, p = .001) and social AT (r = .16, p = .002) measured in adulthood. Correlations for non-social AT did not achieve significance in males. Furthermore, there was no significant longitudinal association in AT observed for males or females. Despite the constraints of using different measures and different raters at the two ages, this study found modest developmental stability of social AT from early childhood to adulthood in boys.

Maternal characteristics predicting young girls' disruptive behavior

Little is known about the relative predictive utility of maternal characteristics and parenting skills on the development of girls' disruptive behavior. The current study used five waves of parent- and child-report data from the ongoing Pittsburgh Girls Study to examine these relationships in a sample of 1,942 girls from age 7 to 12 years. Multivariate generalized estimating equation analyses indicated that European American race, mother's prenatal nicotine use, maternal depression, maternal conduct problems prior to age 15, and low maternal warmth explained unique variance. Maladaptive parenting partly mediated the effects of maternal depression and maternal conduct problems. Both current and early maternal risk factors have an impact on young girls' disruptive behavior, providing support for the timing and focus of the prevention of girls' disruptive behavior.

Heritability of verbal and performance intelligence in a pediatric longitudinal sample

The longitudinal stability of IQ is well-documented as is its increasing heritability with age. In a longitudinal twin study, we addressed the question to what extent heritability and stability differ for full scale (FSIQ), verbal (VIQ), and performance IQ (PIQ) in childhood (age 9-11 years), and early adolescence (age 12-14 years). Genetic and environmental influences and correlations over time were evaluated in an extended twin design, including Dutch twins and their siblings. Intelligence was measured by the Wechsler Intelligence Scale for children - Third version (WISC III). Heritability in childhood was 34% for FSIQ, 37% for VIQ, and 64% for PIQ, and increased up to 65%, 51%, and 72% in early adolescence. The influence of common environment decreased between childhood and early adolescence from explaining 43% of the phenotypic variance for FSIQ to 18% and from 42% for VIQ to 26%. For PIQ common environmental influences did not play a role, either in childhood or in early adolescence. The stability in FSIQ and VIQ across the 3-year interval (r(p)) was .72 for both measures and was explained by genetic and common environmental correlations across time (FSIQ, r(g) = .96, r(c) = 1.0; VIQ, r(g) =.78, r(c) = 1.0). Stability of PIQ (r(p) =.56) was lower and was explained by genetic influences (r(g) = .90). These results confirm the robust findings of increased heritability of general cognitive abilities during the transition from childhood to adolescence. Interestingly, results for PIQ differ from those for FSIQ and VIQ, in that no significant contribution of environment shared by siblings from the same family was detected.

Pre-divorce problems in 3-year-olds: a prospective study in boys and girls

OBJECTIVE

We examined to what extent internalizing and externalizing problems at age 3 preceded and predicted parental divorce, and if divorce and the time lapse since divorce were related to internalizing and externalizing problems at age 12.

METHODS

Parental ratings of internalizing and externalizing problems were collected with the Child Behavior Checklist (CBCL) in a large sample (N = 6,426) of 3-year-old children. All these children were followed through the age of 12 years, at which parents completed the CBCL again, while teachers completed the Teacher's Report Form. Children whose parents divorced between age 3 and age 12 were compared with children whose families remained intact.

RESULTS

Girls whose parents divorced between ages 3 and 12 already showed more externalizing problems at age 3 than girls whose parents stayed married. Higher levels of externalizing problems in girls at age 3 predicted later parental divorce. Parental reports indicated that 12-year-olds with divorced parents showed more internalizing and externalizing problems than children with married parents. Levels of teacher-reported problems were not different between children with married versus divorced parents. However, children whose parents divorced between ages 3 and 12 showed more teacher-rated internalizing problems at age 12 when the divorce was more recent than when the divorce was less recent. Parental ratings of both internalizing and externalizing problems at age 12 were not associated with the time lapse since divorce.

CONCLUSION

Externalizing problems in girls precede and predict later parental divorce. Post-divorce problems in children vary by raters, and may depend on the time lapse since divorce.